Pickups have been used for a long time as transducers for converting musical sounds, i.e., the vibrations of strings of a musical instrument, into electrical signals in order to process the signals and reproduce the sounds in an amplified form. Such pickups, which often incorporate rigid piezoelectric crystals to convert vibrations into electrical signals, are mounted under the saddle of a stringed instrument. The crystals are sandwiched between a reference voltage and contacts. Leads connect to the contacts, and wires are connected to each of the leads at one end and to an amplifier at the other end.
By way of example, a typical guitar 10 is shown in FIG. 1. The guitar has a front side 14, a body 16, a neck 18 attached to the body, and a standard tuning mechanism 22 at a free end of the neck. The front side 14 has a sound board 24 with a bridge assembly 26 mounted on it. There are six strings 30 extending from distal ends 30a connected to tuning posts 32, over a saddle assembly 34 and into a bridge plate 36 at their proximal ends 30b which are also fastened by posts 40.
FIG. 2 shows a semi-schematic enlarged end view, in partial cross section, of a bridge assembly 26. For each string 30, pressure from the normal mounting of the string pulls saddle 34 forward (in the direction of arrow A) and down so that the saddle sits in the tilted position as shown. When the string is plucked or otherwise played, the string's vibrations are transferred to the saddle. The vibratory movement of the saddle is transferred to a transducer or pickup 42, which underlies and is in contact with the saddle. The pickup incorporates a piezoelectric element, which converts the vibratory motion of the saddle into an electrical signal which is carried by pickup wires 44 to an amplifier (not shown). The signal is then processed, as is well known in the art, to reproduce the string's sound at speakers.
An example of a pickup incorporating piezoelectric crystals is shown in U.S. Pat. No. 4,657,114 to Shaw, which is directed to a combination saddle and pickup. In the pickup, six piezoelectric crystals are held in spaced relation by a rigid frame. On top of the crystals is a common (ground) conductor connected to an upper face of each crystal. The lower face of each crystal is pressed against a conductor so that an electrical signal is generated by each of the crystals is response to the vibrations transferred from the saddle. The signals pass from the crystals to six contact elements, respectively, located below the conductor and in registry with the crystals. The contact elements sit on a PC board, which has leads on it for each contact element, which leads carry the sensed voltages to wires which bend and pass through a hole in the bridge plate and the guitar top to the inside of the guitar where they connect to an amplifier jack.
In such a pickup, the frame and PC board create rigid and thick structure, which i,s conventionally used to provide support for the elements, and to electrically shield the leads, among other reasons. Due to this rigid structure, the wires are necessary for flexibility in order to be bent as needed to pass from the undersaddle portion of the pickup into the guitar body and to connect the leads to the amplifier jack.
The wires are normally soldered to the leads. The solder joints are cumbersome to make and can often come apart with very little tension on the wires or leads, e.g., due to any movements of the pickup or wires. Once such a connection breaks, it is virtually impossible to repair, and a new pickup is required. The problem of loose connections of the leads to the wires has plagued amplified acoustic guitars and other stringed instruments for quite some time. The problem is particularly acute where the pickup is multiphonic, that is, where the pickup has separate contacts and leads for each string. In a six-stringed guitar, connecting six wires to six leads is quite cumbersome. Often, as in U.S. Pat. No. 5,123,325 to Turner, coaxial cables or multiple axial cables are connected to the leads to minimize the number of wires used and to provide some shielding of the signals in the wires from each other. Still, interconnection of the leads with the wires is cumbersome, and the strength of the connection is weak.
The lead connection problem also exists in undersaddle pickups, which are separately manufactured from the saddle as opposed to Shaw's combined saddle and pickup.
Another problem with undersaddle pickups is that the relatively thick structure of a typical undersaddle pickup requires that when retrofitting a guitar with a pickup, the saddle must be replaced or cut so that the new or modified saddle is at the same height when sitting on the pickup as the old saddle was without the pickup.
A further problem with a conventional undersaddle pickup assembly arises from the fact that, due to the static pressure of the string, i.e., the pressure at which the string is strung, the saddle is tilted. This tilt results in only a line-type contact between the saddle and pickup 42 at front edge 46 of the saddle. The saddle typically will be tilted about 2.degree. under maximum string pressure, but this could be up to about 3.degree. to 5.degree., or even 10.degree., in some instruments. The amount of tilt can be reduced by more snugly installing the saddle in the bridge, but this too severely impedes translation of vibrations from the strings to the transducer. Therefore, guitar manufacturers typically provide 0.004" to 0.008" of total play between the saddle and bridge walls of amplified acoustic instruments to accommodate shrinking and swelling of the bridge slot due to ambient temperature and humidity to ensure that the saddle can freely move up and down to transfer the strings' static load evenly to the pickup.
The problem which results from the tilted saddle is that the line-type contact, e.g., at front edge 46, is often near the front edge of the pickup. This means that the line of contact may be at the edge or beyond the edge of the piezoelectric elements which are not normally as wide as the pickup, because the pickup's housing and insulation is provided on each side of the piezoelectric elements. Thus, there is a very limited contact area between the saddle and pickup due to the tilted saddle, and there is the possibility that the saddle contact line will be outside or at the very edge of the piezoelectric elements. This results in poor translation of the saddle's static pressure to the piezoelectric elements for any elements with which the line of contact is not in registry. More importantly, where there are multiple elements in the pickup, there will inevitably be some misalignment between piezoelectric elements due to manufacturing tolerances. Accordingly, some elements will be in registry with the line of contact, and some will not. The resultant problem is that the static load on each crystal will be different, depending upon whether it is underneath or not underneath the line of contact.
Because the output level of the electric signal from a piezoelectric material varies with the static load on the material, the uneven pressure will create uneven string balance in the signal output from each element. Furthermore, the line-type contact of the saddle with the pickup results in high pressure on the pickup due to the small area of contact, which can shatter or damage the piezoelectric element when this contact is near the edge of the element, particularly where the element is circular. Therefore, it is desirable to make the static load on each crystal consistent.
The aforementioned problem of too snugly installing the saddle also impedes the even translation of the strings' static load to the pickup.
A further problem is that pickup assemblies are relatively thick and spongy due to use of a skeletal structure, substantial foil or shielding means, solid piezocrystal or PVDF film, and thus they will absorb and damp some of the strings' available energy that would otherwise be transmitted to the guitar body. For example, in U.S. Pat. No. 5,155,285 to Fishman, an undersaddle pickup, in one embodiment, is formed by a circuit board having fiberglass and copper clad layers, a carbon fiber strip below the circuit board, a piezoelectric (PVDF) sheet, a metal sheet as a ground plane, and an outer shield of paper and paint wrapping. The paper and paint wrapping give the structure a spongy quality, even though the circuit board and metal sheet are rigid. Since it is desirable for the guitar body to receive as much of the strings' vibrations as possible to enhance the volume and quality of the guitar's acoustic output, the absorption and dampening of the vibrational energy transfer by such a thick, spongy pickup will adversely affect the guitar's acoustic output.
An additional problem with undersaddle pickups is fitting the pickup to the instrument's saddle (or bridge slot) thickness, since the saddle thickness varies depending upon the instrument. For example, in acoustic guitars saddle thicknesses of 0.093, 0.110, 0.125, and 0.187 inch exist with 0.093 and 0.125 inch being the most common in the Unites States. Currently, undersaddle pickups come in two very different models to accommodate the two common slot sizes. The different models require different equipment and assembly lines to manufacture. Moreover, fitting the non-common slot sizes with an undersaddle pickup requires substantial work on the saddle slot, or a custom undersaddle pickup. Rather than undertake these measures, often one simply uses one of the two standard size pickups, e.g., the pickup for an 0.093 inch thick saddle with a 0.110 inch saddle or the pickup for a 0.125 saddle with a 0.187 inch saddle. This leaves so much play between the pickup and the bridge slot walls that it is difficult to reliably position the pickup such that the forward edge 46 of the saddle 34 will contact the pickup at or near the centerline for the pickup. This exacerbates the line contact problem discussed above.
In view of the foregoing, what is needed is an undersaddle pickup which is thin so as to minimize the adverse affect on the acoustics of the instrument, and which does not suffer from the assembly problem of connecting leads to wires and from the attendant problems of an unreliable connection of the wires with the leads, and bulkiness of the wires. These problems are particularly acute where hexaphonic pickups are used because there are six leads. What is also needed is a pickup and saddle assembly in which the static pressure on each piezoelectric element is consistent. What is further needed is a pickup that once it is installed, the string-to-string volume may be easily adjusted by external electronic controls for the following purposes: (1) to compensate for the often imperfect craftsmanship found in production guitars and in aftermarket installations; (2) to adjust for changes to the guitar's structure due to changes in ambient temperature and humidity; and (3) to suit the individual musician's artistic taste. What is further needed is an undersaddle pickup that is easy and inexpensive to manufacture in numerous sizes.